Improvement in caissons for sinking piers



.JAMES B. EADS, OF ST. LOUIS, MISSOURI.

IMPROVEMENT IN CAISSONS FOR SINKING PlERS.

Specification forming part of Letters Patent No. 118,118, dated Augustl5, 1871.

To all whom it may concern:

Be it known. that I, JAMES B. EADS, of St. Louis, in the county et St.Louis and State of Missouri, have invented certa-in new and usefulImprovements in Caissons for Sinking' Piers, of which the following is aspecication:

My invention consists, first, in placing the airlocl: either partialiyor wholly within the main air-chamber of the caisson; and secondly, inthe use ofa water-tight air-sh aft to communicate with the air-chamber,whereby the outer skin or caisson inclosing the masonry may be dispensedwith.

Figure l shows, partly in elevation and partly in longitudinal section,the caisson and lower portion of the pier, the section being taken onthe line Y Y, Fie. 2. Fig. 2 is a horizontal section .at the line X X,Fig. l. Fig. 3 shows, half in elevation and half in section, at the lineZl Z, Fig. et, the caisson and lower portion of the pier, the shaftscommunicating with the air-lock being placed outside the masonry andthecaisson extended ateach end beneath the shaft. Fig. 4 is a horizontalsection at the line Z Z, Fig. 3.

A is the `shell of the caisson, which extends both upward and downwardfrom the horizontal top B ofthe air-chamber. O are girders ruiming fromend of the caisson and attached to the top B and the sides. D arebrackets also attached to both top and sides of the air-chamber,imparting rigidity to the structure. The caisson, besides its partialsupport by the pressure of air beneath it, rests upon the broad bases ofthe girders C and upon a course of timber, E, which is extended aroundthe inner side of the shell. c are apertures in the girder C to allowthe passage of the workmen from one compartment of the airehamber toanother. =,Ffis'tlle""I''iisomy of the pier. Gare-watertight shaftswhose upper ends are open to the air, and which may be made of metal,wood, or other suitable substance. These shafts extend verticallythrough or beside the masonry, and their lower ends communicate, by

A a manhole, J, with an air-loch, K. The air-lock communicates, by aman-hole, L, with the interior of the main air-chamben rI he man-holes JandL have doors J and L whose edges are made closed. The air-locks aregenerally about ve feet in diameter and from seven to twelve feet high.Both doors J and L are made to open toward the main air-ch amber, sothat the extra or plenal pressure of air will always keep one or both ofthe doors closed.

Previous to the introduction of my improvement the air-lock was placedat the upper end of Y a vertical shaft which was in direct communicationwith the air-chamber of the caisson, and, as the caisson descended andthe masonry was built up, the shaft was increased in height by theaddition of sections thereto; for this purpose the air-lock had to beremoved from the shaft and the compressed air permitted to escape fromthe main air-chamber and shaft, the water and mud entering to take theplace of the air and rendering the whole interior wet and dirty, theworkmen remaining idle while the sectional addition was made to theshaft and the water again forced from the air-chamber. Thus theair-chamber an d shaft were continually kept in an unhealthy condition,calculated to injuriously aifect the operatives. This shaft constitutedan element of danger, as it furnished a chamber for the reception of thewhole amount of air contained in the caisson, in case ofthe lattersubsidin g rapidly from any cause, such as entering a quicksand; in thiscase the workmen might not have sufficient warning to enable them toreach the shaft, and their lives would be sacriticed.

My lock, bein g placed in the air-ch amber, leaves no space (as theshaft before mentioned) for the escape of air .under extraordinarypressure, and on any rapid subsidence of the caisson the men could notbe deprived of air, the air being limited to half the space, exertin gdouble the raising power upon the caisson, and so checking its descent.The position I give to the air-locks ena-- bles the connnunicationbetween the pier-top and the air-chamber to be made by means of shaftswhose tops are open to the outer air. The shaft-s may be built even withthe top ofthe pier during construction, or be kept somewhat in advancethereof, and may be made of wood, metal, or any materia-l foundsuitable, either wood or metal answering the purpose satisfactorily.' Bymaking the shafts water-tight l am enabled to dispense with the outerskin of the caisson inclosing the masonry, the said skin being builtonly of suicient height to form a coder-dani, if any is needed, at thefirst setting of the caisson in position. When the water-tight skin ofthe caisson inolosin g the masonry is built up, as the pier de scends soas to keep the skin above the waterlevel, the shafts communicating withthe air-locks need not be water-tight; but the construction of this skininvolves great expense, and the difiiculty is so great of rendering itwater-tight against the extreme pressure of the water that any meansenabling this skin to be dispensed with is valuable. This end isaccomplished by making my shafts water-tight to exclude the water whichpercolates through the joints of the masonry.

In some cases the piers have insuflicient area to admit of shafts beingmade in the body of the masonry without seriously weakening thestructure. In such cases I locate the water-tight airshafts outside themasonry, as shown in Figs. 3 and 4, the caisson having extensions Albeneath the shafts so as to clear a way for the descent of the saidshafts, the said extensions being of any y suitable form.

Where the excavation is made in sand or fine gravel (even if some largerstones are found) the made through coarse' gravel, clay, and largerstones these matters are removed by a dredge which operates in a shaftopen at top and bottom and extending from above the water-level to apoint below the caisson.

Neither the means for removal of the excavated material nor the pumpsfor forcing air into the air-chamber are shown, as these provisions arewell understood and constitute no part of my present improvement.

I do not claim an air-lock applied at the lower end of a pneumatic pile,as described in a patent granted to F. E. Sickles on the 1st ofFebruary, 1870, independently of a caisson for con strncting piers.

The following is what I claim as new: y

l. In connection or combination with a caisson for sinking piers ofmasonry or other material,

the airlock K placed at or near the bottom. of the air-shaft'Gr andpartially or wholly within the air-chamber of said caisson,substantially as herein set forth.

2. The extensions A of the caissons, substantially as and for thepurpose set forth.

In testimony of which invention I hereunto set my hand.

Witnesses:

SAML. KNIGHT, Gno. C. FABIAN.

JAS. B. EADS.

